Discrete Element Simulation if Crack Initiation and Damage Evolution in Concrete

To investigate the damage evolution process in concrete, numerical simulations were conducted using the Discrete Element Method(DEM) to study crack initiation and propagation evolution in pre- cracked concrete specimens under different loading modes. Based on the aggregate geometry in concrete materials, a three-dimensional discrete element model incorporating irregular polyhedral aggregates was developed. The flat-joint model was then employed to investigate crack initiation and propagation behavior in concrete specimens under four loading modes, revealing the meso-scale damage mechanisms underlying macroscopic failure in concrete. The results demonstrate that:(1) During the initial loading phase, fewer internal cracks were observed in the concrete specimen. Due to the compressive stress concentration effect, shear cracks predominantly clustered near both loading ends, while tensile cracks initiated at the pre-existing crack tip. In the later loading stage, cracks rapidly propagated along aggregate boundaries, resulting in crack deflection. Secondary cracks emerged adjacent to the loading ends and extended towards the specimen mid-section, accompanied by limited crack development within highly stressed aggregates.(2) As the loading angle increased from 0° to 28°, the proportion of shear cracks at the pre- existing crack tip exhibited an increasing trend, demonstrating the transition from tensile-dominated to shear-dominated failure mechanisms in concrete. However, tensile failure remained the predominant factor governing specimen failure across all four loading modes.(3) Within the loading angle range of 0°-28°, the crack initiation angle at the pre-existing crack tip exhibited a positive correlation with increasing loading angles. The predictions based on the generalized maximum tangential stress(GMTS) criterion showed good agreement with simulation results for pure Mode I and mixed Mode Ⅰ-Ⅱ loading conditions, while demonstrating higher predictions under pure Mode Ⅱ loading.